The aim of the work is to characterize the effects of randomly induced mutations on fitness in populations of Drosophila melanogaster. Mutations will be induced on the X-chromosome with ethyl methanesulfonate (EMS) and X-rays. Their effects will be ascertained in single and multiple generation experiments. In the former, the influence of the mutants on survival will be measured; in the latter, attention will be focused on total fitness effects. Of course, total fitness includes survival, but it involves other componenets, such as fertility, as well. One goal is to determine the connection between the survival effects and the overall fitness effects of the induced mutants. Another is to compare the effects of chemical and radiation-induced mutations. A third is to explore the possibility that the total fitness effects vary from one generation to another, and if so, randomly or otherwise.